The following is an abstract from Wikipedia.
Moen is a manufacturer of faucets and other fixtures founded by inventor Al Moen. The company is headquartered in North Olmsted, Ohio.
It was originally part of Ravenna Metal Products of Seattle, Washington. In 1956, it became part of Stanadyne, Inc., which was in turn acquired by Forstmann-Little & Company in 1988. Today, Moen is part of consumer-products holding company Fortune Brands.
Moen Faucet design
Most faucets (kitchen, lavatory, and bathtub/shower) are of the single-handle design, and almost all have used the same basic water-controlling cartridge since the 1960s. Known as the Moen 1225, it is a plastic (older versions were brass) cylinder approximately 4 inches long by 3/4 inches in diameter. As the “engine” in most Moen single-handle faucets, it has undergone at least two revisions since its inception though newer versions remain compatible with older faucets. Pulling up the stem of the cartridge opens the water supply; rotating toward the left opens the hot water passages while rotating to the right opens the cold water passages (using the standard North American convention of the hot water control on the left).
Later Moen bathtub/shower controls with single handles use a larger cartridge with a pressure balancing mechanism which compensates for sudden pressure changes in either the hot or cold water supply (as caused by a toilet being flushed while someone is showering). The design goal is to maintain the temperature of the shower for safety and comfort reasons, even if the volume of water is reduced. The cartridge is known as the 1222. The operation is similar to the 1225 (above) though the cartridge is approximately 1 inch in diameter to allow space for the pressure balancing mechanism.
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